Replacement of split-pin assemblies in nuclear reactor

Abstract

A pin-insertion/torque tool has a blade in a loading tube, which blade is vertically moveable axially by a hydraulic cylinder and can rotate for proper pin alignment. The tool includes a laterally open wrench having splines capable of engaging splines on the new nut. The new split pin is mounted on the blade by a long tube in the end of which the pin is threaded. Once on the blade the tube is unthreaded from the pin. The pin-insertion/torque tool is then moved to a position precisely set by a stop centered along the axis of the hole joining the counterbores in the LGT. The blade is raised thus inserting the new split pin through the lower counterbore and through hole and into the new nut which was deposited in the upper counterbore of the LGT by a pick-and-put tool. The wrench is then repeatedly engaged with the splines in the nut laterally of the 'mousehole' into which the nut extends and is rotated, by a hydraulic cylinder and a rack and pinion, over a limited angle. The mechanism which rotates the wrench resets the wrench precisely at the same point in space at the beginning of each stroke. There is clearance between the railing edge of the wrench and the 'mousehole' at the beginning of each stroke and between the leading edge of the wrench and the 'mousehole' at end of each stroke. A hold-down arm for the new nut is provided. The rotation of the nut threads the nut onto the split pin and draws the split pin into the lower counterbore. Low torque is applied until the nut is stalled on the base of the upper counterbore and then high torque of precise magnitude is applied to secure the nut.